U.S. patent application number 16/708462 was filed with the patent office on 2020-08-06 for piezoelectric sensor and method for manufacturing the same.
This patent application is currently assigned to Sumitomo Riko Company Limited. The applicant listed for this patent is Sumitomo Riko Company Limited. Invention is credited to Wataru TAKAHASHI.
Application Number | 20200245947 16/708462 |
Document ID | / |
Family ID | 1000004558320 |
Filed Date | 2020-08-06 |
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United States Patent
Application |
20200245947 |
Kind Code |
A1 |
TAKAHASHI; Wataru |
August 6, 2020 |
PIEZOELECTRIC SENSOR AND METHOD FOR MANUFACTURING THE SAME
Abstract
A piezoelectric sensor (10) having an elongated-sheet shape
includes a piezoelectric layer (11) containing an elastomer and
piezoelectric particles and electrode layers (12a and 12b) which
are disposed with the piezoelectric layer (11) sandwiched between
the electrode layers. In the piezoelectric sensor (10), a pressure
sensing region (S) has a length of 500 mm or longer in a
longitudinal direction thereof; the electrode layers (12a and 12b)
contain an elastomer and flaky conductive materials and are capable
of elongating by 10% or more in one direction of plane directions;
and when a space between one end portion (A) and the other end
portion (B) of the pressure sensing region (S) in the longitudinal
direction is set as a measurement zone, an electrical resistance in
the measurement zone in the electrode layers (12a and 12b) is
3,000.OMEGA. or lower, and the specific Expression (I) is
satisfied.
Inventors: |
TAKAHASHI; Wataru; (Aichi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sumitomo Riko Company Limited |
Aichi |
|
JP |
|
|
Assignee: |
Sumitomo Riko Company
Limited
Aichi
JP
|
Family ID: |
1000004558320 |
Appl. No.: |
16/708462 |
Filed: |
December 10, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2019/012105 |
Mar 22, 2019 |
|
|
|
16708462 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 41/0478 20130101;
A61B 5/1102 20130101; A47C 21/00 20130101; A61B 5/6892 20130101;
H01L 41/37 20130101; H01L 41/183 20130101; H01L 41/1132 20130101;
H01L 41/29 20130101; H01L 41/0533 20130101; A61B 5/113
20130101 |
International
Class: |
A61B 5/00 20060101
A61B005/00; H01L 41/047 20060101 H01L041/047; H01L 41/053 20060101
H01L041/053; H01L 41/113 20060101 H01L041/113; H01L 41/18 20060101
H01L041/18; H01L 41/29 20060101 H01L041/29; H01L 41/37 20060101
H01L041/37; A47C 21/00 20060101 A47C021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2019 |
JP |
2019-015731 |
Claims
1. A piezoelectric sensor having an elongated-sheet shape,
comprising: a piezoelectric layer containing an elastomer and
piezoelectric particles; and electrode layers which are disposed
with the piezoelectric layer sandwiched between the electrode
layers, wherein, when a region in which the electrode layers
overlap each other via the piezoelectric layer is set as a pressure
sensing region, the pressure sensing region has a length of 500 mm
or longer in a longitudinal direction thereof, wherein the
electrode layers contain an elastomer and flaky conductive
materials and are capable of elongating by 10% or more in one
direction of plane directions, and when a space between one end
portion and the other end portion of the pressure sensing region in
the longitudinal direction is set as a measurement zone, an
electrical resistance in the measurement zone in the electrode
layers is 3,000.OMEGA. or lower, and wherein, when the electrode
layers disposed with one piezoelectric layer sandwiched
therebetween are set as a first electrode layer and a second
electrode layer, the following Expression (I) is satisfied.
(Young's Modulus of Piezoelectric Layer.times.Thickness of
Piezoelectric Layer).gtoreq.{(Young's Modulus of First Electrode
Layer.times.Thickness of First Electrode Layer)+(Young's Modulus of
Second Electrode Layer.times.Thickness of Second Electrode Layer)}
(I)
2. The piezoelectric sensor according to claim 1, wherein
sensitivity of the piezoelectric sensor is 50 pC/N or higher.
3. The piezoelectric sensor according to claim 1, wherein the flaky
conductive materials contained in the electrode layers comprise
flaky carbon materials.
4. The piezoelectric sensor according to claim 3, wherein the
electrode layers further contain a dispersant.
5. The piezoelectric sensor according to claim 3, wherein a content
of the flaky carbon material content is 20 parts by mass or more
and 45 parts by mass or less when the entire electrode layers are
set as 100 parts by mass.
6. The piezoelectric sensor according to claim 1, further
comprising: a protective layer that is stacked on at least one of
the electrode layers and contains an elastomer.
7. The piezoelectric sensor according to claim 6, wherein a product
of Young's modulus and a thickness of the protective layer is
larger than a product of Young's modulus and a thickness of the
electrode layer adjacent to the protective layer.
8. The piezoelectric sensor according to claim 1, wherein peeling
strength of the electrode layers with respect to the piezoelectric
layer is 2 N/25 mm or higher.
9. A method for manufacturing piezoelectric sensor, which
manufactures the piezoelectric sensor according to claim 1 and
comprises: a coating-film forming step in which a conductive
coating material for forming the electrode layers is coated on a
surface of a base member by a die-coating method or a dispenser
method to form an electrode-layer forming coating film; and a
press-attaching step in which the electrode-layer forming coating
film and the piezoelectric layer are overlapped and press-attached
before cross-linking of the formed electrode-layer forming coating
film is completed.
10. The method for manufacturing piezoelectric sensor according to
claim 9, wherein at least one of a press machine, a vacuum press
machine, a roll press machine, and a thermocompression laminator is
used in the press-attaching step.
11. The method for manufacturing piezoelectric sensor according to
claim 9, wherein a surface of the electrode-layer forming coating
film which is attached to the piezoelectric layer has an arithmetic
average roughness (Ra) of 6 .mu.m or lower.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of
International Application number PCT/JP2019/012105, filed on Mar.
22, 2019, which claims the priority benefit of Japan Patent
Application No. 2019-015731, filed on Jan. 31, 2019. The entirety
of each of the above-mentioned patent applications is hereby
incorporated by reference herein and made a part of this
specification.
BACKGROUND
Technical Field
[0002] The present disclosure relates to a piezoelectric sensor
being elongated and flexible and including a piezoelectric layer
and an electrode layer which contain an elastomer.
Related Art
[0003] A piezoelectric material that can convert mechanical energy
into electrical energy is widely used in pressure sensors,
acceleration sensors, vibration sensors, impact sensors, or the
like. The piezoelectric material may be ceramics such as lead
zirconate titanate (PZT), a polymer such as polyvinylidene fluoride
(PVDF) or polylactic acid, a complex obtained by filling a polymer
matrix with piezoelectric particles, or the like.
[0004] In recent years, with a purpose of healthcare or detection
and medical treatment of diseases, or in order to estimate a health
condition of a driver in a driver monitoring system, a technology
in which a piezoelectric sensor using a piezoelectric material is
used to measure biological information such as a respiratory
condition or a heart rate has been developed.
[0005] For example, as a device that measures biological
information of a sleeping subject, a biological information
measuring panel including bottom boards made of silicone rubber and
a piezoelectric film sensor that detects strain of the bottom board
which is produced due to biological activity of the subject is
disclosed in Patent Literature 1. [Literature of related art]
PATENT LITERATURE
[0006] Patent Literature 1: Japanese Patent Laid-Open No.
2014-124310 [0007] Patent Literature 2: International Publication
No. WO2017/010135 [0008] Patent Literature 3: Japanese Patent
Laid-Open No. 2018-56287 [0009] Patent Literature 4: Japanese
Patent Laid-Open No. 2015-210927 [0010] Patent Literature 5:
International Publication No. WO2017/169627
[0011] As disclosed in Patent Literature 1, in order to measure
biological information of the sleeping subject, a measurement
device is disposed to extend in a shoulder-width direction of the
subject. In this case, when the measurement device is inflexible,
the subject feels discomfort such as hardness or stiffness when the
subject lies on the measurement device. Additionally, the subject
is conscious of a piezoelectric sensor, and thus there is a concern
that it is not possible to accurately measure a heart rate or sleep
is disturbed.
[0012] In this respect, the biological information measuring panel
disclosed in Patent Literature 1 employs the bottom boards made of
silicone rubber. Besides, the piezoelectric sensor is disposed
between two bottom boards so as not to overlap the subject, and the
piezoelectric sensor detects strain of the bottom boards which is
produced due to biological activity of the subject. Here, an
installation location of the piezoelectric sensor is not below the
subject. That is, vibration produced due to the biological activity
of the subject reaches the piezoelectric sensor through the bottom
board. However, the bottom board made of silicone rubber has
viscoelasticity, and thus the vibration produced due to the
biological activity of the subject is significantly attenuated
during a period in which the vibration is transmitted to the
piezoelectric sensor. Therefore, it is difficult to detect weak
vibration of respiration and heartbeats with high accuracy.
[0013] Even when the subject moves by turning over while sleeping,
in order to accurately detect biological information thereof, it is
desirable to use an elongated piezoelectric sensor so that the
piezoelectric sensor overlaps the subject. In this case, an
electrode layer is also formed into an elongated shape. A terminal,
to which wiring or the like is connected, is usually disposed at
one end portion of the electrode layer. Here, when the electrode
layer has an elongated shape, a problem arises in that an
electrical resistance increases and conductivity decreases in a
direction separated (far apart) from the terminal. When the
electrical resistance of the electrode layer is high (conductivity
is low), electromotive voltage generated in the piezoelectric layer
is lowered in the electrode layer, and an output voltage is low. In
other words, sensitivity of the piezoelectric sensor is reduced. In
view of the problem, a countermeasure for increasing an amount of a
conductive material in the electrode layer is considered. However,
when the amount of the conductive material increases, the electrode
layer hardens (Young's modulus increases), and flexibility of the
electrode layer and the piezoelectric sensor is inhibited.
[0014] Patent Literatures 2 and 3 disclose a flexible piezoelectric
sensor including a piezoelectric layer and an electrode layer which
contain an elastomer. Patent Literatures 2 and 3 describe volume
resistivity of the electrode layer from the viewpoint of
maintaining conductivity even during elongation; however, there is
no sprit for forming a piezoelectric sensor into an elongated
shape. Therefore, Patent Literatures 2 and 3 do not provide a study
on the problem of a decrease in conductivity which occurs when the
electrode layer is formed into an elongated shape and do not
provide a suggestion for solving the problem either.
[0015] Patent Literature 4 discloses, as a conductive film used as
an electrode layer of a transducer or the like, a conductive film
that contains an elastomer and a conductive material and has a
smooth surface with arithmetic average roughness (Ra) of less than
0.5 .mu.m. Patent Literature 4 discloses that the conductive film
is formed to have a smooth surface, and thereby it is possible to
improve adhesiveness to a counterpart member so as to suppress
peeling; however, there is no sprit for forming the electrode layer
into an elongated shape. Patent Literature 5 discloses, as a
conductive film used as an electrode layer of a transducer or the
like, a conductive film that contains an elastomer and flaky carbon
materials and has surface glossiness of higher than 0.4% and lower
than 10%. Patent Literature 5 discloses that the flaky carbon
materials are oriented along a surface of the conductive film, and
thereby it is possible to increase conductivity and maintain high
conductivity even during elongation; however, there is no sprit for
forming the electrode layer into an elongated shape.
[0016] The present disclosure is made with consideration for such a
circumstance, and an object thereof is to provide a flexible
piezoelectric sensor that has a small decrease in conductivity in
an electrode layer even when the piezoelectric sensor is elongated
and thus has a good sensitivity.
SUMMARY
[0017] (1) In order to achieve the object described above, a
piezoelectric sensor of the present disclosure has an
elongated-sheet shape, the piezoelectric sensor including a
piezoelectric layer containing an elastomer and piezoelectric
particles and electrode layers which are disposed with the
piezoelectric layer sandwiched between the electrode layers; when a
region in which the electrode layers overlap each other via the
piezoelectric layer is set as a pressure sensing region, the
pressure sensing region has a length of 500 mm or longer in a
longitudinal direction thereof; the electrode layers contain an
elastomer and flaky conductive materials and are capable of
elongating by 10% or more in one direction of plane directions, and
when a space between one end portion and the other end portion of
the pressure sensing region in the longitudinal direction is set as
a measurement zone, an electrical resistance in the measurement
zone in the electrode layers is 3,000.OMEGA. or lower; when the
electrode layers disposed with one piezoelectric layer sandwiched
therebetween are set as a first electrode layer and a second
electrode layer, the following Expression (I) is satisfied.
(Young's Modulus of Piezoelectric Layer.times.Thickness of
Piezoelectric Layer).gtoreq.{(Young's Modulus of First Electrode
Layer.times.Thickness of First Electrode Layer)+(Young's Modulus of
Second Electrode Layer.times.Thickness of Second Electrode Layer)}
(I)
(2) A method of manufacturing the piezoelectric sensor of the
present disclosure includes a coating-film forming step in which a
conductive coating material for forming the electrode layers is
coated on a surface of a base member by a die-coating method or a
dispenser method to form an electrode-layer forming coating film
and a press-attaching step in which the electrode-layer forming
coating film and the piezoelectric layer are overlapped and
press-attached before cross-linking of the formed electrode-layer
forming coating film is completed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a view of disposition of a piezoelectric sensor
being an embodiment of the present disclosure.
[0019] FIG. 2 is a top view of the piezoelectric sensor.
[0020] FIG. 3 is a sectional view taken along line III-III in FIG.
2.
DESCRIPTION OF THE EMBODIMENTS
[0021] (1) The piezoelectric sensor of the present disclosure is a
sensor having an elongated-sheet shape and includes a pressure
sensing region having a length of 500 mm or longer. Therefore, when
the piezoelectric sensor of the present disclosure is disposed on
bedding to measure biological information of ansubject, the
pressure sensing region easily overlaps a part of the subject's
body. Thus, it is possible to detect without missing weak vibration
due to respiration and heartbeats. In the present disclosure, when
a length of the piezoelectric sensor is 500 mm or longer, the
piezoelectric sensor is described to have an "elongated" shape.
[0022] When the pressure sensing region has a length of 500 mm or
longer, the electrode layers have the same length as the length of
the pressure sensing region. Conventionally, when the piezoelectric
sensor has an elongated shape as described above, conductivity
decreases in a direction separated from one end portion of the
electrode layer at which a terminal is disposed, and it is not
possible to realize a desired sensor sensitivity at the entire
pressure sensing region. In this respect, the electrode layers that
configure the piezoelectric sensor of the present disclosure
contain an elastomer and flaky conductive materials. The flaky
conductive materials have a relatively high aspect ratio
(length/thickness). Therefore, even when a blending amount of the
flaky conductive materials does not increase too much, the flaky
conductive materials easily come into contact with each other, and
a conduction path is easily formed. Therefore, while flexibility is
secured, an electrical resistance is unlikely to increase even when
the length of the electrode layers increases, and high conductivity
can be maintained. Specifically, the electrical resistance in a
measurement region (between the one end portion and the other end
portion in a longitudinal direction) in the electrode layers is
3,000.OMEGA. or lower. Additionally, when the flaky conductive
materials are oriented in a manner that a length direction thereof
is coincident with a plane direction of the electrode layer, the
conductivity can be further increased, and the conduction path is
unlikely to be cut even during elongation. As described above, the
piezoelectric sensor of the present disclosure includes the
electrode layer having high conductivity from one end portion to
the other end portion and thus has high sensitivity even in an
elongated shape.
[0023] The electrode layer is capable of elongating by 10% or more
in one direction of the plane directions and has good flexibility
in that the previous Expression (I) is satisfied. Since the
electrode layer is flexible, the electrode layer can be deformed
following deformation such as bending, and a load can be accurately
transmitted to a piezoelectric layer. This is also effective in
improving sensitivity of the piezoelectric sensor. In addition,
satisfaction of (I) means that a ratio of an external force applied
to the piezoelectric layer with respect to an external force
applied to the piezoelectric sensor increases. In this case, in
accordance with the following Expression (II), a quantity of
electric charge generated in the piezoelectric layer increases. The
quantity of generated electric charge is proportional to sensor
output. In other words, when Expression (I) is satisfied, the
sensor output increases. Quantity of Generated Electric Charge (C)
in
Piezoelectric Layer=Sensor Sensitivity (C/N).times.External Force
Applied to Piezoelectric Layer (II)
In addition, even when the piezoelectric sensor of the present
disclosure is disposed on bedding and the subject lies on the
bedding, the subject is unlikely to feel a discomfort such as
hardness or stiffness. Additionally, the piezoelectric sensor is
capable of extending and contracting following movement of the
subject or the bedding. Therefore, it is possible to precisely
detect weak vibration due to respiration and heartbeats or a
respiratory sound derived from the respiration and the
heartbeats.
[0024] (2) In a method for manufacturing the piezoelectric sensor
of the present disclosure, first, a die-coating method or a
dispenser method is used to form an electrode-layer forming coating
film. A conductive coating material for forming the electrode layer
contains flaky conductive materials. The flaky conductive materials
are dispersed in a liquid conductive coating material in random
directions. When the conductive coating material is coated on a
base member, if the die-coating method and the dispenser method are
used, a shear force is applied to the conductive coating material.
The flaky conductive materials contained in the conductive coating
material are oriented by the shear force in a manner that the
length direction of the flaky conductive material is coincident
with a forming direction of the coating film, that is, the length
direction of the flaky conductive materials is horizontal with
respect to a surface of the coating film. Consequently, a
conduction path is easily formed in the longitudinal direction of
the electrode layer. As a result, the electrical resistance is
unlikely to increase even when the length of the electrode layers
increases, and high conductivity can be realized. In addition, when
the flaky conductive materials are oriented, unevenness on the
surface of the coating film decreases, an adhering area with the
piezoelectric layer increases and adhesiveness can be increased.
When the unevenness on the surface of the electrode layer
decreases, a gap between the piezoelectric layer and the electrode
layer decreases, and thus the sensitivity of the piezoelectric
sensor effectively improves.
[0025] Subsequently, in the method for manufacturing the
piezoelectric sensor of the present disclosure, the coating film
and the piezoelectric layer are overlapped and press-attached to
each other before cross-linking of the formed electrode-layer
forming coating film is completed. Consequently, the surface of the
coating film is further smoothened, the adhering area with the
piezoelectric layer increases and the adhesiveness can be further
increased. When the adhesiveness is high, the piezoelectric layer
and the electrode layers are unlikely to peel off even when
extending and contracting are repeated, and thus durability of the
sensor improves. As described above, according to the manufacturing
method of the present disclosure, the adhering area of the
electrode layers with the piezoelectric layer increases and the
adhesiveness can be improved. Hence, an elongated piezoelectric
sensor having high sensitivity can be manufactured.
[0026] As an embodiment of a piezoelectric sensor of the present
disclosure, an example of using a piezoelectric sensor as a
biological information detecting device is described.
[0027] FIG. 1 is a view of disposition of the biological
information detecting device of the embodiment. FIG. 2 is a top
view of the piezoelectric sensor in the biological information
detecting device. FIG. 3 is a sectional view taken along line
III-III in FIG. 2. FIG. 1 is a view through the biological
information detecting device.
[0028] As shown in FIGS. 1 to 3, a biological information detecting
device 1 includes a piezoelectric sensor 10, wiring 20a and 20b,
and a control circuit unit 30. In the embodiment, in a state in
which a subject P sleeps on the back on a mattress, a
shoulder-width direction of the subject P is defined as a
right-left direction, and a height direction thereof is defined as
a front-rear direction. A width of the piezoelectric sensor 10 is a
length in the front-rear direction, and a length thereof is a
length in the right-left direction. The piezoelectric sensor 10 is
fixed to a back side of a cover 40 that covers the mattress of a
bed.
[0029] The piezoelectric sensor 10 is disposed to extend in a
strip-like shape in the right-left direction. A part of the
piezoelectric sensor 10 is disposed below the chest of the subject
P. The piezoelectric sensor 10 has a rectangular-sheet shape having
a width of 50 mm, a length of 900 mm, and a thickness of 0.575 mm
(575 .mu.m). The piezoelectric sensor 10 has an elongated shape and
includes a piezoelectric layer 11, a pair of electrode layers 12a
and 12b, and a pair of protective layers 13a and 13b.
[0030] The piezoelectric layer 11 contains carboxyl group-modified
hydrogenated nitrile rubber (XH-NBR) and lithium sodium potassium
niobate particles. A content of the lithium sodium potassium
niobate particles is 48 volume % when a volume of the XH-NBR is set
as 100%. The piezoelectric layer 11 has a rectangular thin-film
shape having a width of 40 mm, a length of 900 mm, and a thickness
of 0.035 mm (35 .mu.m). The Young's modulus of the piezoelectric
layer 11 is 80 MPa. The piezoelectric layer 11 is subjected to a
polarization treatment, and the lithium sodium potassium niobate
particles are polarized in a thickness direction (up-down
direction) of the piezoelectric layer 11.
[0031] The electrode layer 12a contains glycidyl ether
group-modified acrylic rubber and flaky carbon materials. The
electrode layer 12a has a rectangular thin-film shape having a
width of 40 mm, a length of 900 mm, and a thickness of 0.02 mm (20
.mu.m). The electrode layer 12a is disposed on a top surface of the
piezoelectric layer 11. The wiring 20a is connected to a left end
portion of the electrode layer 12a via a terminal. A material, a
shape, and a size of the electrode layer 12b are the same as those
of the electrode layer 12a. The electrode layer 12b is disposed on
an undersurface of the piezoelectric layer 11. The wiring 20b is
connected to a left end portion of the electrode layer 12b via a
terminal. The electrode layers 12a and 12b are both capable of
elongating by 10% or more in the right-left direction. The Young's
modulus of both the electrode layer 12a and the electrode layer 12b
is 35 MPa. An electrical resistance of a space (measurement region)
between the left end portion (point A in FIG. 2) and a right end
portion (point B in FIG. 2) in the electrode layers 12a and 12b is
675.OMEGA..
[0032] The electrode layers 12a and 12b have the same Young's
modulus and thickness. In other words, when the two electrode
layers disposed with the piezoelectric layer sandwiched
therebetween have the same Young's modulus and thickness, the
previous Expression (I) can be expressed as the following
Expression (Ia).
(Young's Modulus of Piezoelectric Layer.times.Thickness of
Piezoelectric Layer) {(Young's Modulus of Electrode
Layer.times.Thickness of Electrode Layer).times.2} (Ia)
When Expression (Ia) is further transformed, the following
Expression (Ib) is obtained. Thus, a determination on whether
Expression (I) is satisfied can be made by Expression (Ib).
(Young's Modulus of Piezoelectric Layer.times.Thickness of
Piezoelectric Layer)/{(Young's Modulus of Electrode
Layer.times.Thickness of Electrode Layer).times.2}.gtoreq.1
(Ib)
In the embodiment, when values of the Young's moduli and the
thicknesses of the piezoelectric layer 11 and the electrode layers
12a and 12b are substituted in Expression (Ib) to be computed, 2.0
is obtained. In other words, the piezoelectric sensor 10 satisfies
Expression (I).
[0033] The protective layer 13a is made of a thermoplastic
elastomer and has a rectangular thin-film shape having a width of
50 mm, a length of 900 mm, and a thickness of 0.25 mm (250 .mu.m).
The protective layer 13a is disposed on a top surface of the
electrode layer 12a. A material, a shape, and a size of the
protective layer 13b are the same as those of the protective layer
13a. The protective layer 13b is disposed on an undersurface of the
electrode layer 12b. The Young's modulus of both the protective
layer 13a and the protective layer 13b is 20 MPa.
[0034] The piezoelectric layer 11, the electrode layers 12a and
12b, and the protective layers 13a and 13b have the same length and
are different from each other only in width. As shown by hatching
with dotted lines in FIG. 2, when viewed from above, a pressure
sensing region S (region in which the electrode layers 12a and 12b
overlap the piezoelectric layer 11 in the thickness direction) at a
central portion of the piezoelectric sensor 10 in a width direction
thereof. The pressure sensing region S has a width of 40 mm and a
length of 900 mm in the right-left direction (longitudinal
direction).
[0035] The electrode layer 12a and the control circuit unit 30 are
electrically connected via the wiring 20a. The electrode layer 12b
and the control circuit unit 30 are electrically connected via the
wiring 20b. When a load is applied to the piezoelectric sensor 10
due to respiration and heartbeats of the subject P, electric
charges are generated in the piezoelectric layer 11. The generated
electric charges (output signal) are detected as a change in
voltage or current by the control circuit unit 30. The respiration
and heartbeats of the subject are detected based on the detection
of the electric charges.
[0036] In the embodiment, a base material of both the piezoelectric
layer 11 and the electrode layers 12a and 12b which configure the
piezoelectric sensor 10 is an elastomer. In addition, the
protective layers 13a and 13b are also made of an elastomer.
Because each of the layers is flexible, the entire piezoelectric
sensor 10 is flexible. Accordingly, even when the piezoelectric
sensor 10 is disposed on a mattress, and the subject P lies on the
piezoelectric sensor 10, the subject P is unlikely to feel a
discomfort such as hardness or stiffness. In addition, the
electrode layers 12a and 12b contain the flaky carbon materials,
and the electrical resistance between the left end portion and the
right end portion is 675.OMEGA.. Even when the length of the
electrode layers 12a and 12b increases, the electrical resistance
is small. As described above, the piezoelectric sensor 10 includes
the electrode layers 12a and 12b having high conductivity over the
entire length thereof in the longitudinal direction and thus has
high sensitivity even in an elongated shape. Besides, the
piezoelectric sensor 10 is capable of extending and contracting
following movement of the subject P or the mattress, and thus weak
vibration due to the respiration and heartbeats can be precisely
detected even when the subject P overlaps an end portion of the
pressure sensing region S.
[0037] One embodiment of the piezoelectric sensor of the present
disclosure is described above. The piezoelectric sensor of the
present disclosure is not limited to the embodiment described above
and can be implemented in various embodiments in which
modifications and alterations which can be performed by those
skilled in the art are performed within a range without departing
from the gist of the present disclosure.
[0038] <Piezoelectric Layer>
[0039] The piezoelectric layer contains an elastomer and
piezoelectric particles. As the elastomer, at least one selected
from crosslinked rubbers and thermoplastic elastomers may be used.
Flexible elastomers having relative low Young's modulus include
urethane rubber, silicone rubber, nitrile rubber (NBR),
hydrogenated nitrile rubber (H-NBR), acrylic rubber, natural
rubber, isoprene rubber, ethylene-propylene-diene rubber (EPDM),
ethylene-vinyl acetate copolymer, ethylene-vinyl acetate-acrylic
ester copolymer, butyl rubber, styrene-butadiene rubber,
fluoro-rubber, epichlorohydrin rubber, and the like. In addition,
an elastomer modified by introducing a functional group or the like
may be used. Modified elastomers are preferably hydrogenated
nitrile rubbers having at least one group selected from, for
example, a carboxyl group, a hydroxyl group, and an amino
group.
[0040] The piezoelectric particles are particles of a compound
having piezoelectricity. As the compound having piezoelectricity, a
ferroelectric substance having a perovskite crystal structure is
known, and the compound includes, for example, barium titanate,
strontium titanate, potassium niobate, sodium niobate, lithium
niobate, potassium sodium niobate, lithium sodium potassium
niobate, lead zirconate titanate (PZT), barium strontium titanate
(BST), bismuth lanthanum titanate (BLT), strontium bismuth
tantalate (SBT), and the like. One or two or more kinds thereof may
be used as the piezoelectric particles.
[0041] A content of the piezoelectric particles may be determined
with consideration of flexibility of the piezoelectric layer and
the piezoelectric sensor and piezoelectric performance of the
piezoelectric layer. When the content of the piezoelectric
particles increases, the piezoelectric performance of the
piezoelectric layer improves but the flexibility decreases.
Accordingly, in a combination of an elastomer and the piezoelectric
particles to be used, it is preferable to adjust the content of the
piezoelectric particles so as to realize desired flexibility. For
example, the content of the piezoelectric particles may be 30
volume % or more and 50 volume % or less when the elastomer is set
as 100 volume %.
[0042] The piezoelectric layer is manufactured by hardening a
composition under a predetermined condition, the composition being
obtained by adding powder of the piezoelectric particles, a
cross-linker, or the like in an elastomer polymer. Then, the
piezoelectric layer is subjected to a polarization treatment. In
other words, a voltage is applied to the piezoelectric layer, and a
polarization direction of the piezoelectric particles becomes
coincident with a predetermined direction.
[0043] As a result of study, the present inventors verified that
sensitivity to an applied load increases in the sheet-shaped
piezoelectric sensor when a sectional area perpendicular to a
tension direction of the piezoelectric layer is small. Thus, a thin
piezoelectric layer is preferable. For example, the thickness of
the piezoelectric layer is preferably 200 .mu.m or smaller, and
more preferably 100 .mu.m or smaller. On the other hand, when the
piezoelectric layer is too thin, dielectric breakdown is likely to
occur during the polarization treatment. Therefore, the thickness
of the piezoelectric layer is preferably 10 .mu.m or larger, and
more preferably 20 .mu.m or larger.
[0044] <Electrode Layer>
[0045] The electrode layer contains an elastomer and the flaky
conductive materials. The kind of elastomer, the kind and the
content of the flaky conductive materials, and the like may be
appropriately determined so that the flexibility and the
conductivity of the electrode layer are balanced. In terms of
flexibility, the electrode layer is configured to elongate by 10%
or more in one direction of plane directions. For example,
"elongate by 10% in one direction" means that the length of the
electrode layer in the direction is 1.1 times of the length in a
no-load state. Besides, when the electrode layers disposed with one
piezoelectric layer sandwiched therebetween are set as a first
electrode layer and a second electrode layer, the following
Expression (I) is satisfied.
(Young's Modulus of Piezoelectric Layer.times.Thickness of
Piezoelectric Layer) {(Young's Modulus of First Electrode
Layer.times.Thickness of First Electrode Layer)+(Young's Modulus of
Second Electrode Layer.times.Thickness of Second Electrode Layer)}
(1)
In this specification, the Young's modulus is calculated from a
stress-elongation curve obtained by performing a tensile test
prescribed in JIS K 7127: 1999. The tensile test is performed using
a test piece type 2 at a tensile speed of 100 mm/min.
[0046] In terms of conductivity, when a region in which the
electrode layers overlap each other via the piezoelectric layer is
set as a pressure sensing region, and a space between one end
portion and the other end portion of the pressure sensing region in
the longitudinal direction is set as a measurement zone, the
electrical resistance in the measurement zone in the electrode
layers is 3,000.OMEGA. or lower. When the electrical resistance in
the measurement region is 2,000.OMEGA. or lower and even
1,000.OMEGA. or lower, it is preferable because the conductivity
further increases.
[0047] From the viewpoint of having rubber-like elasticity at
normal temperature, preferably, an elastomer having a
glass-transition temperature (Tg) equal to or lower than room
temperature is used as the elastomer. Crystallinity decreases as
the Tg decreases. Therefore, the elastomer is more easily extended
and contracted. For example, an elastomer having the Tg of
0.degree. C. or lower, -10.degree. C. or lower, or even -30.degree.
C. or lower is more flexible and is preferable.
[0048] The elastomer is preferably a crosslinked rubber from a
reason that the crosslinked rubber has good resilience when
deformation is repeated. In addition, an elastomer that has a
microphase-separated structure having a hard segment and a soft
segment and is pseudo-crosslinked like a thermoplastic elastomer
may be used. The thermoplastic elastomers include an olefin-based
elastomer, a styrene-based elastomer, a polyester-based elastomer,
an acrylic-based elastomer, a urethane-based elastomer, or a
PVC-based elastomer. Crosslinked rubbers include urethane rubber,
acrylic rubber, silicone rubber, butyl rubber, butadiene rubber,
ethylene oxide-epichlorohydrin copolymer, nitrile rubber (NBR),
hydrogenated nitrile rubber (H-NBR), chloroprene rubber, natural
rubber, isoprene rubber, styrene-butadiene rubber,
ethylene-propylene-diene copolymer (EPDM), polyester rubber, or
fluoro-rubber. In addition, an elastomer that is modified, like
epoxidized natural rubber or carboxyl group-modified hydrogenated
nitrile rubber, by introducing a functional group or the like may
be used. Among the above rubbers, acrylic rubber has low
crystallinity and a weak intermolecular force and thus has a lower
Tg compared with other kinds of rubber. Thus, acrylic rubber is
flexible and elongated easily.
[0049] The flaky conductive material may be appropriately selected
from flaky metal materials and flaky carbon materials. The flaky
metal material include silver, gold, copper, nickel, rhodium,
palladium, chromium, titanium, platinum, iron, an alloy thereof,
metal oxide consisting of zinc oxide, titanium oxide and the like,
metal carbide consisting of titanium carbonate and the like. The
flaky carbon material can be manufactured by a carbon material
having a graphite structure, such as graphite or expanded graphite.
The flaky carbon material is preferably a multilayer graphene which
is a stack of a plurality of layers of graphene. The graphene is
one layer of graphite and has a structure in which six-membered
rings of carbon atoms are connected into a planer shape. The number
of stacks of graphene in the multilayer graphene is smaller than
that of graphite and is preferable several layers to hundreds of
layers.
[0050] For example, when the flaky carbon material is used, the
content of the flaky carbon material is 20 parts by mass or more
and 45 parts by mass or less when the entire electrode layers are
set as 100 parts by mass. When the content of the flaky carbon
material is less than 20 parts by mass, it is difficult for the
flaky carbon materials to come into contact with each other, and
sufficient conduction paths cannot be formed. Conversely, when the
content of the flaky carbon material is more than 45 parts by mass,
the Young's modulus of the electrode layer increases, and the
flexibility decreases. When the Young's modulus of the electrode
layer increases, the ratio of the external force applied to the
piezoelectric layer decreases. Hence, the previous Expression (I)
is not satisfied, leading to a decrease in the sensor
sensitivity.
[0051] The electrode layer may contain additives such as a
cross-linker, a cross-linking promoter, a cross-linking aid, a
plasticizer, a processing aid, an antioxidant, a softener, a
colorant, and the like. The cross-linker, the cross-linking
promoter, and the cross-linking aid which contribute to a
cross-linking reaction may be appropriately selected depending on
the type of the elastomer. When the plasticizer is contained,
low-temperature resistance of the electrode layer improves. The
plasticizers include adipic acid diester, ether-ester derivative,
and the like.
[0052] When the flaky carbon materials are used, it is preferable
to blend the dispersant in order to suppress clumping of the flaky
carbon materials and improve dispersibility. The dispersants
include polymer surfactant (for example, high-molecular-weight
polyester acid amidoamine salt or the like) having an organic salt
structure in which an anion and a cation are ion-bonded to each
other, a polymer formed by an amide bond or an imide bond between a
polycyclic aromatic component and an oligomer component, and the
like.
[0053] In a case of the former high-molecular-weight polyester acid
amidoamine salt, amine groups are adsorbed onto the flaky carbon
materials, and a dispersibility improving effect is exerted. In
addition, an influence on the conductivity decreases, and a surface
of the electrode layer is easily smoothened.
[0054] The polycyclic aromatic component in the latter polymer has
a .pi.-.pi. interaction and contributes to an affinity with the
flaky carbon material. The polycyclic aromatic component has a
multi-ring structure including an aromatic ring. The number and the
arrangement of rings are not particularly limited. Preferably, the
polycyclic aromatic component has, for example, any one of a
benzene ring, a naphthalene ring, an anthracene ring, a
phenanthrene ring, a pyrene ring, a perylene ring, and a
naphthacene ring. With consideration of the flexibility, a biphenyl
structure in which the benzene rings are connected to each other or
a structure having the naphthalene rings is preferable. The
oligomer component having the amide bond or the imide bond with the
polycyclic aromatic component contributes to affinity with the
elastomer. The oligomer component compatible with the elastomer is
preferable.
[0055] The adhesiveness between the piezoelectric layer and the
electrode layer influences the sensitivity and the durability of
the piezoelectric sensor. The high adhesiveness between the
piezoelectric layer and the electrode layer is achieved due to an
increase in adhering area between the two layers. When the adhering
area increases, electric charges generated in the piezoelectric
layer can be output without leaking from the electrode layer. In
addition, when the adhesiveness is high, the piezoelectric layer
and the electrode layers are unlikely to peel off even when the
extending and contracting are repeated, and thus the durability of
the sensor improves. From the viewpoint of increasing adhesiveness,
a peeling strength of the electrode layer with respect to the
piezoelectric layer is preferably 2 N/25 mm or higher.
[0056] In this specification, the peeling strength is measured by
performing a 90.degree. peeling test in accordance with "10. 4
measurement of peel adhesion" in JIS Z 0237: 2009, and an average
value of measured values of peeling forces under a peeling length
of 100 mm when the peeling lengths range from 25 mm to 125 mm is
adopted. The 90.degree. peeling test is performed in a condition of
a tensile width of 25 mm and a tensile speed of 300 mm/min under
room temperature.
[0057] <Protective Layer>
[0058] From the viewpoint of protecting an insulation property of
the piezoelectric sensor and suppressing damage caused by
mechanical stress from outside, a protective layer may be disposed
to be stacked on at least one of the electrode layers. Here, from
the viewpoint that the protective layer increases strain of the
piezoelectric layer and improves the sensitivity of the sensor
without restricting deformation of the piezoelectric layer and the
electrode layers, it is preferable that the protective layer
contains an elastomer. For example, the protective layer may be
disposed at one or both outer sides in a stacking direction of a
stack of the piezoelectric layer and the electrode layers. In
addition, when a plurality of units in which the piezoelectric
layer is installed between a pair of electrode layers is stacked,
the protective layer may be disposed between the electrode layers
adjacent in the stacking direction.
[0059] For example, when a force is applied in the stacking
direction of the stack of the piezoelectric layer and the electrode
layers (when the piezoelectric sensor is compressed), the
protective layer elongates in the plane direction, and thereby a
shear force acts on the piezoelectric layer and the electrode
layers. Consequently, a tensile force in the plane direction is
applied to the piezoelectric layer in addition to a pressing force
in the stacking direction, and the strain of the piezoelectric
layer increases. As a result, a quantity of electric charges
generated in the piezoelectric layer increases, and the sensitivity
of the sensor improves. The lower the Young's modulus of the
protective layer, the more remarkable a sensitivity improving
effect obtained by the protective layer. On the other hand, when a
large shear force acts on the piezoelectric layer and the electrode
layers, there is a concern that durability of both layers
decreases. Therefore, from the viewpoint of durability, it is
preferable that a product of the Young's modulus and a thickness of
the protective layer is larger than a product of the Young's
modulus and a thickness of the adjacent electrode layer, as
described in the following Expression (III).
(Young's Modulus of Protective Layer.times.Thickness of Protective
Layer) >(Young's Modulus of Electrode Layer.times.Thickness of
Electrode Layer) (III)
[0060] One or more elastomers selected from crosslinked rubbers and
thermoplastic elastomers may also be used as the elastomer of the
protective layer. Elastomers which are relatively low in Young's
modulus and flexible and have a good adherence property to the
electrode layer include natural rubber, isoprene rubber, butyl
rubber, acrylic rubber, silicone rubber, urethane rubber, urea
rubber, fluoro-rubber, NBR, and the like. In particular, when human
biological information is measured, it is preferable to use
silicone rubber or urethane rubber having an excellent affinity
with a living body, and it is preferable that the elastomer do not
contain a substance such as the plasticizer which dissolves out
with time.
[0061] In order to decrease a change in sensitivity of the sensor
when the sensor is repeatedly used, the protective layer preferably
has excellent slumping resistance. In addition, the protective
layer preferably has good wear durability and good tear durability
to play a role of protecting the piezoelectric sensor from external
mechanical stress.
[0062] A Poisson's ratio of the elastomer is about 0.5. Therefore,
in the protective layer made of elastomer, a force applied in the
thickness direction directly acts as a force in the plane
direction. Therefore, the larger the thickness of the protective
layer, the more a strain increasing effect of the piezoelectric
layer increases, and the more the sensitivity improving effect of
the sensor increases.
[0063] On the other hand, when the thickness of the protective
layer increases, the thickness of the piezoelectric sensor
increases, and the discomfort felt by the subject increases when
the piezoelectric sensor is used as a biological information
sensor. Therefore, a thickness of each one of the protective layers
may be, for example, 5 .mu.m or larger and 1,000 .mu.m or smaller.
In this specification, the thickness of the protective layer is a
thickness of a region of one layer of the protective layers, the
region being stacked on the electrode layer, as shown by a
reference sign T in FIG. 3 described above.
[0064] <Piezoelectric Sensor>
[0065] The piezoelectric sensor has an elongated-sheet shape. A
size of the piezoelectric sensor is not particularly limited as
long as the piezoelectric sensor has an elongated size, that is, a
length of 500 mm or longer. It is sufficient that at least the
pressure sensing region in which the electrode layers overlap each
other via the piezoelectric layer has a length of 500 mm or longer
in a longitudinal direction thereof. When the pressure sensing
region has a small width, the sensitivity decreases and it is
difficult to detect weak vibration. The width of the pressure
sensing region is preferably 10 mm or larger and more preferably 40
mm or larger. Conversely, when the pressure sensing region has a
large width, the sensitivity increases; however, when the
piezoelectric sensor is used as the biological information sensor,
there is a concern that the discomfort felt by the subject
increases, or air permeability is degraded and the subject is
likely to sweat. The preferable width is 200 mm or smaller. The
longer the length of the pressure sensing region, that is, the
higher a rate of the length to the width, the more easily the
subject's body overlaps the pressure sensing region, and thus the
more easily the weak vibration due to respiration and heartbeats is
detected. The preferable length is 550 mm or larger. On the other
hand, from the viewpoint of easy installation on the bedding, the
preferable length is 1,000 mm or shorter. When the pressure sensing
region has a large thickness, the discomfort felt by the subject
increases. The thickness is preferably 5 mm or smaller and even 2
mm or smaller.
[0066] The sensitivity of the piezoelectric sensor of the present
disclosure is preferably 50 pC/N or higher. When the sensitivity is
50 pC/N or higher, the piezoelectric sensor is suitable as a
biological information sensor that detects the weak vibration of
the respiration or the heartbeats. In this specification, the
sensitivity of the sensor is a value obtained by dividing a
quantity of electric charges (C/m.sup.2) generated per unit area by
a load (N/m.sup.2) applied per unit area.
[0067] <Method for Manufacturing Piezoelectric Sensor>
[0068] A manufacturing method of the present disclosure, which is
one preferable method for manufacturing the piezoelectric sensor of
the present disclosure, includes a coating-film forming step and a
press-attaching step. Hereinafter, the steps will be described.
[0069] (1) Coating-Film Forming Step
[0070] This step is a step in which a conductive coating material
for forming the electrode layers is coated on a surface of a base
member by a die-coating method or a dispenser method to form an
electrode-layer forming coating film.
[0071] The conductive coating material may be prepared by
dispersing and dissolving a material (polymer of elastomer, flaky
conductive materials, or the like) for forming the electrode layer
in a solvent. The elastomer and the flaky conductive material are
as described above. It is preferable that the solvent can dissolve
the polymer of elastomer. For example, it is preferable to use
butyl cellosolve acetate, acetylacetone or the like as the solvent.
The conductive coating material may contain additives such as a
cross-linker, a cross-linking promoter, a cross-linking aid, a
dispersant, a plasticizer, a processing aid, an antioxidant, a
softener, a colorant, an antifoaming agent, a leveling agent, a
viscosity modifier and the like. The cross-linker, the
cross-linking promoter, and the cross-linking aid which contribute
to a cross-linking reaction may be appropriately selected depending
on the kind of the elastomer. The plasticizer and the dispersant
are as described above. When the flaky conductive materials
contained in the electrode layer are flaky carbon materials, the
conductive coating material may be prepared by the following two
methods.
[0072] (i) First Preparation Method
[0073] The first preparation method includes a step of preparing a
liquid composition containing an elastomer polymer, at least one of
graphite powder and expanded graphite powder, and a solvent and a
step of crushing the liquid composition using a wet jet mill.
[0074] Powder of natural graphite or artificial graphite may be
used as the graphite powder. Powder of flake-formed graphite
subjected to a flake forming process may be used. The expanded
graphite is obtained by inserting a substance between layers of
scale-like graphite, the substance generating gas when being
heated. The expanded graphite powder may be the natural graphite or
the artificial graphite. Powder of flake-formed expanded graphite
subjected to the flake forming process may be used as the expanded
graphite powder.
[0075] According to the wet jet mill, the liquid composition is
pressurized by a high-pressure pump, sent into a nozzle and ejected
from the nozzle at a high speed. Then, the graphite powder and the
like in the liquid composition are crushed by a high shear force
which is generated when the liquid composition passes through the
nozzle, cavitation, and an impact force caused by impact with a
wall or impact between the liquid compositions. According to the
wet jet mill, peeling is easily proceed because the shear force is
applied to the graphite powder or the expanded graphite powder.
Consequently, it is possible to easily obtain nanometer-order
multilayer graphene (flaky carbon materials). Processing pressure,
a type of the nozzle, a nozzle diameter, the number of times of
processing, and the like of the wet jet mill may be appropriately
adjusted so that a desired flaky carbon material is obtained. From
the viewpoint of proceeding the flake formation, a nozzle having a
shape that easily causes the impact with the wall or the impact
between the liquid compositions, for example, an impact (cross)
nozzle or the like, may be selected as the type of the nozzle.
Besides, it is preferable to repeat the crushing two or more times.
In other words, it is preferable to eject the liquid composition
from the nozzle of the wet jet mill two or more times.
[0076] (ii) Second Preparation Method
[0077] The second preparation method includes a step in which
graphite-powder dispersion liquid containing at least one of the
graphite powder and the expanded graphite powder and a solvent is
crushed using the wet jet mill and a step in which an elastomer
solution containing the elastomer polymer and a solvent is added to
the graphite-powder dispersion liquid subjected to the crushing to
prepare the liquid composition.
[0078] The second preparation method is different from the first
preparation method in that the graphite-powder dispersion liquid
instead of the liquid composition is subjected to the crushing. The
crushing performed by the wet jet mill is the same as that in the
first preparation method. It is preferable that the solvent of the
graphite-powder dispersion liquid is the same as the solvent of the
elastomer solution. In addition, when a dispersant is used in the
second preparation method, it is preferable that the dispersant is
blended with the graphite-powder dispersion liquid.
[0079] The base member that is coated with the conductive coating
material is not particularly limited as long as the electrode-layer
forming coating film can be formed by the die-coating method or the
dispenser method. For example, the base member includes a resin
film consisting of polyethylene terephthalate (PET), polyethylene
naphthalate (PEN), polyimide, polyethylene and the like. The base
member is preferably a base member subjected to a release treatment
so that the formed electrode-layer forming coating film easily
peels off.
[0080] The coating of the conductive coating material is performed
by the die-coating method or the dispenser method. The flaky
conductive materials are dispersed in the liquid conductive coating
material in random directions. When the die-coating method and the
dispenser method are used, a shear force in one direction is
applied to the conductive coating material. The flaky conductive
materials contained in the conductive coating material are oriented
by the shear force in a manner that the length direction thereof is
coincident with the forming direction of the coating film, that is,
the length direction of the flaky conductive materials is
horizontal with respect to the surface of the coating film.
Consequently, a conduction path is easily formed in the
longitudinal direction of the electrode layer. As a result, the
electrical resistance is unlikely to increase even when the length
of the electrode layers increases, and high conductivity can be
realized. In addition, when the flaky conductive materials are
oriented, unevenness of the surface of the coating film decreases,
an adhering area with the piezoelectric layer increases and
adhesiveness can be increased. When the unevenness of the surface
of the electrode layer decreases, a gap between the piezoelectric
layer and the electrode layer decreases, and thus the sensitivity
of the piezoelectric sensor is effectively improved. Among the
die-coating methods, a lip die-coating method is preferably used
from a reason that it is possible to apply a large shear force to
the conductive coating material.
[0081] In this step, after the conductive coating material is
coated, the coating film may be heated or the like at a
predetermined temperature to be appropriately dried. However, the
coating film should be used in the next press-attaching step in a
state that cross-linking of the coating film is not completed. In
other words, the electrode-layer forming coating film formed in
this step is in a non-cross-linked or cross-linking proceeding
state (hereinafter, appropriately referred to as a
"half-cross-linked state").
[0082] As described above, when the surface, which is among the
surfaces of the electrode-layer forming coating film and is
press-attached to the piezoelectric layer, has low unevenness, the
adhering area with the piezoelectric layer increases, and the
adhesiveness increases. Accordingly, surface roughness (arithmetic
average roughness: Ra) of the electrode-layer forming coating film
formed in this step is preferably 6 .mu.m or lower.
[0083] (2) Press-Attaching Step
[0084] This step is a step in which the electrode-layer forming
coating film and the piezoelectric layer are overlapped and
press-attached before cross-linking of the electrode-layer forming
coating film formed in the previous step is completed.
[0085] In this step, the half-cross-linked electrode-layer forming
coating film formed in the previous step and the piezoelectric
layer are press-attached. The surface of the electrode-layer
forming coating film is further smoothened by the press-attaching.
Consequently, the adhering area with the piezoelectric layer
further increases, and the adhesiveness can be further increased.
When the adhesiveness is high, in addition to improvement in
sensitivity of the piezoelectric sensor, the piezoelectric layer
and the electrode layers are unlikely to peel off even when
extending and contracting are repeated, and thus durability of the
sensor improves. Preferably, any one or more of a press machine, a
vacuum press machine, a roll press machine, and a thermocompression
laminator is used in the press-attaching. For example, preferably,
the press-attaching is performed in a condition of a temperature of
50.degree. C. or higher and 140.degree. C. or lower and a pressure
of 50 kPa or higher and 300 kPa or lower. In addition, as described
above, from the viewpoint of increasing adhesiveness between the
piezoelectric layer and the electrode layer, the peeling strength
of the electrode layer with respect to the piezoelectric layer is
preferably 2 N/25 mm or higher. The cross-linking of the
electrode-layer forming coating film is completed by the
press-attaching, and the electrode layer is formed.
EXAMPLES
[0086] Next, examples are provided to specifically describe the
present disclosure.
[0087] (1) Relationship between Electrode Layer and Sensor
Sensitivity Six types of piezoelectric sensors were manufactured by
modifying the electrode layers, and sensor sensitivity of the
sensors was measured.
[0088] <Manufacturing of Piezoelectric Layer>
[0089] First, 100 parts by mass of carboxyl group-modified
hydrogenated nitrile rubber ("Therban (registered trademark)
XT8889" manufactured by Lanxess) serving as the elastomer were
dissolved in acetylacetone to prepare a polymer solution. Next, 350
parts by mass of single-particle powder of lithium sodium potassium
niobate serving as the piezoelectric particles were added and
kneaded in the prepared polymer solution. Subsequently, the kneaded
product repeatedly passed through three rolls for five times, and
slurry was obtained. Then, 5 parts by mass of
tetrakis(2-ethylhexyloxy)titanium of the cross-linker were added to
the obtained slurry and kneaded by an air agitator, and then the
slurry is coated on the base member by the die-coating method. A
PET film subjected to the release treatment was used as the base
member. A die coater (manufactured by Techno Machine Co., Ltd) was
used in the coating of the slurry. The coating film was heated at
150.degree. C. for one hour, and a piezoelectric layer having a
thickness of 35 jam was manufactured. The content of the
piezoelectric particles in the piezoelectric layer is 48 volume %
when the elastomer is set as 100 volume %.
[0090] The single-particle powder of lithium sodium potassium
niobate that was used was manufactured as follows.
[0091] (1) First Mixing Step
[0092] As a raw material, powders of K.sub.2CO.sub.3,
Na.sub.2CO.sub.3, Nb.sub.2O.sub.5, and Li.sub.2CO.sub.3 were used.
The powders were weighed based on a composition of a target
sintered body (Li.sub.0.06L.sub.0.047Na.sub.0.47Nb.sub.1.0)O.sub.3
and, then, were wet-mixed in anhydrous acetone for 16 hours. The
obtained mixed powder was subjected to evaporation and was further
dried in an oven, and acetone is volatilized.
[0093] (2) Temporary Firing Step
[0094] The mixed powder obtained after the volatilization of
acetone was put into an alumina crucible, and the crucible was put
in one big crucible. The inner crucible was disposed in a face-down
state so as to cover the mixed powder. The double crucibles are put
in an electric furnace, and temporary firing was performed at
910.degree. C. for ten hours.
[0095] (3) Second Mixing Step
[0096] The obtained temporarily-fired product was crushed into
powder in a mortar. The powder was mixed in anhydrous acetone for
16 hours. The obtained mixed powder was subjected to evaporation
and was further dried in an oven, and acetone is volatilized.
[0097] (4) Final Firing Step
[0098] Similarly to (2), the mixed powder after the volatilization
of acetone was put in double crucibles and was fired at 150.degree.
C. for one hour, at 550.degree. C. for three hours, and at
1,082.degree. C. for a half hour.
[0099] (5) Crushing Step
[0100] The obtained fired product was crushed into single particles
in a ball mill, and single-particle powder of lithium sodium
potassium niobate was obtained.
[0101] <Manufacturing of Electrode Layer>
[Electrode Layer 1]
[0102] First, 35 parts by mass of flake-formed graphite powder, 25
parts by mass of dispersant, 6 parts by mass of cross-linker, and 1
part by mass of cross-linking promoter were added to the polymer
solution obtained by dissolving 68 parts by mass of glycidyl ether
group-modified acrylic rubber polymer serving as the elastomer in
butyl cellosolve acetate, and the conductive coating material was
prepared (the materials are described later in detail). Next, the
prepared conductive coating material was crushed by the wet jet
mill ("Nanovater (registered trademark)" manufactured by Yoshida
Machine Kogyo Co., Ltd). The crushing was performed six times in
total by pass driving (six-pass process). In the first pass, the
crushing was performed in a straight nozzle (having a nozzle
diameter of 170 .mu.m) with a processing pressure of 90 MPa, and in
the second and the following passes, the crushing was performed in
a cross nozzle (having a nozzle diameter of 170 .mu.m) with a
processing pressure of 130 MP. The conductive coating material
obtained after the crushing is coated on the base member by the
die-coating method. The PET film subjected to the release treatment
was used as the base member. The die coater (same as above) was
used in the coating of the conductive coating material. The coating
film was heated at 150.degree. C. for ten minutes, and an electrode
layer 1 having a thickness of 20 .mu.m was manufactured. At this
time, that is, before the coating film is press-attached to the
piezoelectric layer, the cross-linking of the electrode layer 1 is
not completed (the same applies to electrode layers 2 to 5 below
using an elastomer polymer). Hereinafter, the electrode layer 1 at
this time is referred to as the "half-cross-linked" electrode layer
1 in some cases.
[0103] The glycidyl ether group-modified acrylic rubber polymer was
manufactured by suspension polymerization of three kinds of
monomers. Ethyl acrylate (EA), acrylonitrile (AN), and allyl
glycidyl ether (AGE) were used as the monomers. As for a blending
ratio of the monomers, the ratio of EA is set to 96 mass %, the
ratio of AN is set to 2 mass %, and the ratio of AGE is set to 2
mass %. The Tg of the obtained acrylic rubber polymer was
-10.degree. C.
[0104] As the flake-formed graphite powder, "iGurafen-.alpha."
(having an average particle size of 87.2 .mu.m) manufactured by
Itec Co., Ltd was used. As the dispersant, the
high-molecular-weight polyester acid amidoamine salt ("Disparlon
(registered trademark) DA7301" manufactured by Kusumoto Chemicals,
Ltd) was used. As the cross-linker, amino-terminated
butadiene-acrylonitrile copolymer ("ATBN1300.times.16" manufactured
by CVC Thermoset Specialties Ltd.) was used. As the cross-linking
promoter, a zinc complex ("XK-614" manufactured by KING INDUSTRIES,
INC) was used.
[0105] [Electrode Layer 2]
[0106] First, as the flaky conductive materials, 300 parts by mass
of primary silver particles ("Nanomelt Ag-XF301S" manufactured by
FUKUDA METAL FOIL & POWDER CO., LTD) and 50 parts by mass of
secondary silver particles ("FA-STG-111" manufactured by DOWA
Electronics Materials Co., Ltd) were added to a polymer solution
obtained by dissolving 100 parts by mass of epoxy group-containing
acrylic rubber polymer-A ("Nipol (registered trademark) AR51"
manufactured by Nippon Zeon Co., Ltd, Tg: -14.degree. C.) serving
as the elastomer in butyl cellosolve acetate, and the obtained
product is dispersed by three rolls to prepare a conductive coating
material. Subsequently, the conductive coating material is coated
on the base member by the die-coating method. The PET film
subjected to the release treatment was used as the base member. The
die coater (same as above) was used in the coating of the
conductive coating material. The coating film was heated at
150.degree. C. for ten minutes, and the electrode layer 2 having a
thickness of 20 .mu.m was manufactured.
[0107] [Electrode Layer 3]
The electrode layer 3 was manufactured similarly to the electrode
layer 1 except that, in the manufacturing of the electrode layer 1,
a blending amount of the flake-formed graphite powder is increased
to 50 parts by mass, and the zinc complex of the cross-linking
promoter was not blended.
[0108] [Electrode Layer 4]
[0109] First, 10 parts by mass of conductive carbon black
("Ketjenblack EC600JD" manufactured by Lion Corporation), 16 parts
by mass of carbon nanotubes ("VGCF (registered trademark)"
manufactured by Showa Denko K.K.), and 12 parts by mass of
high-molecular-weight polyester acid amidoamine salt (same as
above) serving as the dispersant were added to a polymer solution
obtained by dissolving 100 parts by mass of epoxy group-containing
acrylic rubber polymer-B ("Nipol (registered trademark) AR42 W"
manufactured by Nippon Zeon Co., Ltd, Tg: -26.degree. C.) serving
as the elastomer in butyl cellosolve acetate, and the obtained
product is dispersed by a bead mill to prepare a conductive coating
material. Subsequently, the conductive coating material is coated
on the base member by the die-coating method. The PET film
subjected to the release treatment was used as the base member. The
die coater (same as above) was used in the coating of the
conductive coating material. The coating film was heated at
150.degree. C. for ten minutes, and the electrode layer 4 having a
thickness of 20 .mu.m was manufactured.
[0110] [Electrode Layer 5]
[0111] The electrode layer 5 was manufactured similarly to the
electrode layer 4 except that, in the manufacturing of the
electrode layer 4, the conductive coating material was prepared
without blending carbon nanotubes and the dispersant.
[0112] [Electrode Layer 6]
[0113] Silver paste ("Dotite (registered trademark) D-362"
manufactured by Fujikura Kasei Co., Ltd) is coated on the base
member. The PET film subjected to the release treatment was used as
the base member. The die coater (same as above) was used in the
coating of the conductive coating material. The coating film was
heated at 150.degree. C. for one hour, and the electrode layer 6
having a thickness of 20 .mu.m was manufactured.
[0114] <Manufacturing of Protective Layer>
[0115] A thermoplastic elastomer film ("ESMER (registered
trademark) URS-ET" manufactured by Nihon Matai Co., Ltd and having
a thickness of 250 .mu.m) was cut into a predetermined size, and
the protective layer was obtained.
[0116] <Manufacturing of Piezoelectric Sensor>
[0117] The electrode layers 1 to 6 were combined with the
piezoelectric layer and the protective layer, and six types of
piezoelectric sensors were manufactured as described below. One
piezoelectric sensor has two electrode layers (first electrode
layer and second electrode layer), and the two electrode layers are
the same as each other. The piezoelectric layer and the electrode
layers 1 to 6 are peeled from the base member after overlapping
counterpart members.
[0118] First, a hot-melt film ("ELFAN (registered trademark)
UH-203" manufactured by Nihon Matai Co., Ltd) serving as an
adhesive was attached to the thermoplastic elastomer film of the
protective layer. In the attachment of the film, laminator-A
("LPD3223" manufactured by FUJIPLA Co., Ltd.) was used. Next, the
half-cross-linked electrode layer overlapped the hot-melt film of
the protective layer, and the layer and the film were
press-attached using a vacuum press machine. The press-attaching
was performed in a condition of a temperature of 80.degree. C., a
load of 300 kPa, and a time of 60 seconds. Subsequently, the
piezoelectric layer overlapped the press-attached electrode layer,
and the layers were press-attached using the vacuum press machine
in the same press-attaching condition. Then, the half-cross-linked
electrode layer overlapped the press-attached piezoelectric layer,
and the layers were press-attached using the vacuum press machine
in the same press-attaching condition. Finally, the hot-melt film
of the protective layer overlapped the press-attached electrode
layer, and the film and the layer were press-attached using the
vacuum press machine in the same press-attaching condition.
[0119] As described above, a stack of the protective layer/the
electrode layer/the piezoelectric layer/the electrode layer/the
protective layer was obtained (for convenience of description, an
adhesive layer between the protective layer and the electrode layer
is omitted). A DC power supply was connected to the two electrode
layers of the obtained stack, the polarization treatment was
performed by applying an electric field of 20 V/.mu.m to the
piezoelectric layer for ten minutes, and the piezoelectric sensor
having an elongated-sheet shape was manufactured. The pressure
sensing region in the piezoelectric sensor has a rectangular shape
having a width of 40 mm and a length of 900 mm.
[0120] <Measurement of Young's Modulus>
[0121] The Young's moduli of the piezoelectric layer, the electrode
layer, and the protective layer were calculated from a
stress-elongation curve obtained by performing a tensile test which
is prescribed in JIS K 7127: 1999. The tensile test was performed
by using the test piece type 2 at a tensile speed of 100 mm/min.
From the tensile test, the electrode layers 1 to 5 were verified to
be capable of elongating by 10% or more in the longitudinal
direction. The electrode layer 6 was not capable of elongating up
to 10%.
[0122] <Measurement of Electrical Resistance of Electrode
Layer>
[0123] The electrical resistance between two points in the
longitudinal direction in the pressure sensing region (rectangular
shape having a width of 40 mm and a length of 900 mm) of the
electrode layer was measured. Specifically, a left end portion
(point A in FIG. 2 described above and one end portion in the
present disclosure) was set as a base point (0 mm), points
separated from the base point by 100 mm, 300 mm, 600 mm, and 900 mm
on a straight line in the longitudinal direction were set as
measurement points, and the electrical resistances between the base
point and the measurement points were measured by a tester.
Moreover, the point separated from the base point by 900 mm on a
straight line is a right end portion (point B in the same figure
and the other end portion in the present disclosure) of the
pressure sensing region.
[0124] <Measurement of Sensor Sensitivity>
[0125] The manufactured piezoelectric sensor was installed in a
fatigue durability tester ("MMT-101N" manufactured by Shimadzu
Corporation), and sin waves (frequency of 1 Hz) of loads
2.5N.+-.1.5N, 4.5N.+-.3.5N, and 6.5N.+-.5.5N in a compression
direction were applied in this order to measurement locations
described later by a compression jig (20 mm.times.30 mm). In this
case, an amount of generated electric charges was measured using a
charge amplifier ("NEXUS Charge Amplifier type2692" manufactured by
Briiel & Kjer) and an oscilloscope ("DLM2022" manufactured by
Yokogawa Electric Corporation). Then, an average value was
calculated by dividing the amount of generated electric charges
(unit: Coulomb) measured for each of the loads by an applied
compressive force (unit: Newton) and was set as the sensor
sensitivity (Coulomb/Newton: C/N) at the measurement locations of
the piezoelectric sensor. The measurement locations were set as
four points separated from the base point (point A in FIG. 2
described above) set when the electrical resistance was measured,
the four points being separated from the base point by 100 mm, 300
mm, 600 mm, and 700 mm on a straight line in the longitudinal
direction.
[0126] <Measurement of Sensor Sensitivity During Elongation by
10%>
[0127] The sensor sensitivity at the point separated from the base
point by 100 mm on a straight line in the longitudinal direction
was measured in the same manner as described above except that the
fatigue durability tester (same as above) was installed in a state
that the piezoelectric sensor is elongated by 10% in the
longitudinal direction.
[0128] <Measurement Result>
[0129] Table 1 shows a configuration and sensitivity of the
manufactured piezoelectric sensor, the electrical resistance of the
electrode layer, and the like. In this example, the two electrode
layers disposed at both sides of the piezoelectric layer are the
same as each other. Thus, whether or not the above Expression (I)
is satisfied is determined depending on whether or not a value of
[(Yp.times.Tp)/(Ye.times.Te.times.2)] corresponding to a left side
in the above Expression (Ib) is 1 or larger.
TABLE-US-00001 TABLE 1 Comparative Comparative Comparative
Comparative Piezoelectric sensor Example 1 Example 2 Example 1
Example 2 Example 3 Example 4 Configuration Piezoelectric Young's
80 layer modulus (Yp) [MPa] Thickness 0.035 (Tp) [mm] Electrode
Electrode Electrode Electrode Electrode Electrode layer 1 layer 2
layer 3 layer 4 layer 5 layer 6 Electrode layer Young's 35 20 75 25
2 450 modulus (Ye) [MPa] Thickness 0.02 (Te) [mm] Electrical 38 1
34 317 4917 1> resistance in zone of 100 mm [.OMEGA.] Electrical
225 3 205 1,900 29,500 1> resistance in zone of 300 mm [.OMEGA.]
Electrical 450 6 410 3,800 59,000 1> resistance in zone of 600
mm [.OMEGA.] Electrical 675 9 615 5,700 88,500 1> resistance in
zone of 900 mm [.OMEGA.] Protective layer Young's 20 modulus (Yc)
[MPa] Thickness 0.25 (Tc) [mm] Properties Sensor sensitivity at
point 72 88 44 75 110 25 from one end portion by 100 mm [pC/N]
Sensor sensitivity at point 72 88 44 75 10 25 from one end portion
by 300 mm [pC/N] Sensor sensitivity at point 73 89 44 45 5 25 from
one end portion by 600 mm [pC/N] Sensor sensitivity at point 72 87
44 18 1 or lower 25 from one end portion by 700 mm [pC/N] (Yp
.times. Tp)/(Ye .times. Te .times. 2) 2.0 3.5 0.9 2.8 35.0 0.2
Determination on whether or .smallcircle. .smallcircle. x
.smallcircle. .smallcircle. x not Expression (I) is satisfied
Sensor sensitivity during elongation of 10% (point of 77 83 49 75
115 Indeterminable 100 mm) [pC/N]
[0130] As shown in Table 1, the following was verified. In the
electrode layers 1 and 2 containing the flaky conductive material,
the electrical resistance of the space (the measurement zone)
between both end portions by which a distance between the two
points was the longest was 3,000.OMEGA. or lower, the Young's
modulus was low, and the piezoelectric sensors of Examples 1 and 2
using the electrode layers satisfied the above Expression (I).
Besides, in the piezoelectric sensors of Examples 1 and 2, the
sensitivity was increased to 50 pC/N or higher at any measurement
points, and the high sensitivity was maintained even when the
elongation of 10% was performed. Moreover, when the electrode layer
1 is compared with the electrode layer 2, the electrode layer 2 has
a lower electrical resistance and a higher sensor sensitivity.
However, the electrode layer 2 is formed using the silver particles
as the flaky conductive materials, and thus the cost thereof
increases. Therefore, in application in which the electrode layer
has a large area or the like, it is preferable to use the electrode
layer 1 formed using the carbon materials as the flaky conductive
materials.
[0131] In contrast, the electrode layer 3 contains many flaky
conductive materials. Thus, in the electrode layer 3, the
electrical resistance was low, but the Young's modulus was higher
than the electrical resistance of the electrode layer 1. Therefore,
a piezoelectric sensor of Comparative Example 1 did not satisfy the
above Expression (I). In addition, in the piezoelectric sensor of
Comparative Example 1, the electrode layer 3 was inflexible, and
thus sensitivity decreased. The electrode layers 4 and 5 do not
contain the flaky conductive materials. Thus, in the electrode
layers 4 and 5, the electrical resistance significantly increased
as the distance increased between the two points at which the
electrical resistance was measured. Accordingly, in piezoelectric
sensors of Comparative Examples 2 and 3 using the electrode layers
4 and 5, the sensitivity decreased as the measurement point is
separated from the base point. The electrode layer 6 is made of
silver paste. In the electrode layer 6, the electrical resistance
is low, but the Young's modulus increases, and the electrode layer
is inflexible. Therefore, the electrode layer 6 was not capable of
elongating up to 10%. In addition, a piezoelectric sensor of
Comparative Example 4 using the electrode layer 6 did not satisfy
the above Expression (I), and the sensitivity also decreased.
[0132] (2) Influence of Difference in Manufacturing Method on
Sensor Sensitivity
[0133] With the same configuration and size as that of the
piezoelectric sensor of Example 1 having the electrode layer 1, at
least one of the method for forming the electrode layer 1, a
cross-linking state of the electrode layer 1 before the
press-attaching, and a press-attaching method when the stack is
manufactured is changed to further manufacture seven types of
piezoelectric sensors, and the sensor sensitivity of each
piezoelectric sensor was measured.
Manufacturing of Piezoelectric Sensor
Reference Example 1
[0134] The method for forming the electrode layer 1 was changed to
the lip die-coating method, and the coating of the conductive
coating material was performed using a lip die coater ("test
coater" manufactured by Oriental Packaging Materials Co., Ltd). A
piezoelectric sensor having the electrode layer manufactured in
this way was set as Reference Example 1.
Reference Example 2
[0135] The method for forming the electrode layer 1 was changed to
the dispenser method, and the coating of the conductive coating
material was performed using a dispenser ("air-pulse dispenser"
manufactured by Musashi Engineering Inc). In the dispenser, a flat
nozzle having a slit of 3.0 mm was used. A piezoelectric sensor
having the electrode layer manufactured in this way was set as
Reference Example 2.
Reference Example 3
[0136] The method for forming the electrode layer 1 is changed to a
screen-printing method, and the conductive coating material is
screen-printed on the base member. A piezoelectric sensor having
the electrode layer manufactured in this way was set as Reference
Example 3.
Reference Example 4
[0137] Both the method for forming the electrode layer 1 and the
press-attaching method when the stack is manufactured are changed.
The lip die-coating method was employed, and the coating of the
conductive coating material was performed using the lip die coater
(same as above). Then, the press-attachment of the layers was
performed as follows. First, the half-cross-linked electrode layer
overlapped the hot-melt film of the protective layer, and both the
film and the layer passed between the rolls of a laminator-B
(thermocompression laminator manufactured by MCK) so as to be
press-attached to each other. The press-attaching was performed in
a condition of a temperature of 125.degree. C., a pressure of 196
kPa, and a movement speed of 0.5 m/min. Next, the piezoelectric
layer overlapped the press-attached electrode layer, and the layers
were press-attached using the same device in the same
press-attaching condition. Subsequently, the half-cross-linked
electrode layer overlapped the press-attached piezoelectric layer,
and the layers were press-attached using the same device in the
same press-attaching condition. Finally, the hot-melt film of the
protective layer overlapped the press-attached electrode layer, and
the film and the layer were press-attached using the same device in
the same press-attaching condition. A piezoelectric sensor having
the electrode layer manufactured in this way was set as Reference
Example 4.
Reference Example 5
[0138] Both the method for forming the electrode layer 1 and the
press-attaching method when the stack is manufactured are changed.
The lip die-coating method was employed, and the coating of the
conductive coating material was performed using the lip die coater
(same as above). Then, the press-attachment of the layers was
performed as follows. First, the half-cross-linked electrode layer
overlapped the hot-melt film of the protective layer, and the layer
and the film were press-attached using the laminator-A (same as
above). The press-attaching was performed in a condition of a
temperature of 117.degree. C. and a pressure of 20 kPa. Next, the
piezoelectric layer overlapped the press-attached electrode layer,
and the layers were press-attached using the same device in the
same press-attaching condition. Subsequently, the half-cross-linked
electrode layer overlapped the press-attached piezoelectric layer,
and the layers were press-attached using the same device in the
same press-attaching condition. Finally, the hot-melt film of the
protective layer overlapped the press-attached electrode layer, and
the film and the layer were press-attached using the same device in
the same press-attaching condition. A piezoelectric sensor having
the electrode layer manufactured in this way was set as Reference
Example 5.
Reference Example 6
[0139] Only the cross-linking state of the electrode layer 1 before
the press-attaching was changed. In other words, after the coating
of the conductive coating material was performed using the die
coater, the coating film was heated at 150.degree. C. for one hour,
the cross-linking was completed, and then the stack was
manufactured. A piezoelectric sensor having the electrode layer
manufactured in this way was set as Reference Example 6.
Reference Example 7
[0140] Both the method for forming the electrode layer 1 and the
cross-linking state before the press-attaching changed. The coating
of the conductive coating material was performed by screen
printing. Then, the coating film was heated at 150.degree. C. for
one hour, the cross-linking was completed, and then the stack was
manufactured. A piezoelectric sensor having the electrode layer
manufactured in this way was set as Reference Example 7.
[0141] <Measurement of Surface Roughness of Electrode
Layer>
[0142] As for the coating film of the electrode layer before the
stack was manufactured, the arithmetic average roughness (Ra) of
the surface attached to the piezoelectric layer was measured by a
shape measuring laser microscope (laser microscope) "VK-X100"
manufactured by Keyence corporation. A viewing angle during the
measurement was in a square of 10 mm, and the surface roughness of
the entire square of 10 mm was measured.
[0143] <Measurement of Peeling Strength>
[0144] A sample in which the piezoelectric layer and the electrode
layers were press-attached in a press-attachment width of 25 mm was
prepared in respective press-attachment conditions when the
piezoelectric sensors of Example 1 and Reference Examples 1 to 7
were manufactured. In the samples that are manufactured, the
90.degree. peeling test in accordance with JIS Z 0237: 2009 was
performed (peeling width of 25 mm, peeling length of 100 mm, and
tensile speed of 300 mm/min), and the peeling strength was
measured. Moreover, in the peeling test, when at least one of the
piezoelectric layer and the electrode layer is broken, the test
result was determined as "material breakage".
[0145] <Measurement Result>
[0146] Table 2 collectively shows the coating-film forming step and
the press-attaching step in the method for manufacturing the
piezoelectric sensor, the surface roughness of the electrode layer,
the peeling strength, and the sensitivity of the piezoelectric
sensor.
TABLE-US-00002 TABLE 2 Reference Reference Reference Reference
Reference Reference Reference Example 1 Example 1 Example 2 Example
3 Example 4 Example 5 Example 6 Example7 Electrode Coating-film
forming step Die coating Lip die- Dispenser Screen Lip die- Lip
die- Die coating Screen layer 1 coating printing coating coating
printing Press- Cross-linked state Half-cross- Half-cross-
Half-cross- Half-cross- Half-cross- Half-cross- Cross- Cross-
attaching step of coating film linked linked linked linked linked
linked linked linked Press-attaching Vacuum Vacuum Vacuum Vacuum
Laminator Laminator Vacuum Vacuum method press press press press B
A press press Surface roughness (Ra) [.mu.m] 4.0 3.5 4.5 8.5 3.5
3.5 4.0 8.5 Peeling strength [N/25mm] Material Material Material 1
or Material 1 or 1 or 1 or breakage breakage breakage lower
breakage lower lower lower Properties of Sensor sensitivity at
point from 72 72 71 68 72 69 67 48 piezoelectric one end portion by
100 mm sensor [pC/N] Sensor sensitivity at point from 72 72 71 68
72 69 67 48 one end portion by 300 mm [pC/N] Sensor sensitivity at
point from 73 73 71 68 73 69 66 48 one end portion by 600 mm [pC/N]
Sensor sensitivity at point from 72 72 72 68 72 68 66 48 one end
portion by 700 mm [pC/N]
[0147] As shown in Table 2, when the electrode-layer forming
coating film was formed using the die-coating method, the lip
die-coating method, or the dispenser method, the shear force was
applied to the conductive coating material during the coating, and
thereby a plane of the flaky carbon materials that are contained
was easily oriented along the plane direction of the coating film,
and the surface roughness (Ra) of the coating film decreased to 6
.mu.m or lower. In contrast, when the coating was performed by the
screen-printing method, the shear force is not applied to the
conductive coating material during the coating, orientation depends
on leveling properties of the conductive coating material, and thus
it is difficult for the flaky carbon materials to be oriented.
Therefore, the surface roughness of the coating film increased. As
described in Reference Examples 3 and 7, when the surface roughness
is high, the peeling strength decreases, leading to a decrease in
durability. In addition, a decrease in contact area with the
piezoelectric layer results in a decrease in adhesiveness to the
piezoelectric layer and a decrease in sensor sensitivity.
[0148] When the stack (piezoelectric sensor) is manufactured after
the cross-linking of the electrode-layer forming coating film is
completed, an adhering effect due to pressurizing decreases. Hence,
as shown in Reference Examples 6 and 7, the peeling strength
decreases, leading to a decrease in durability. In addition, the
adhesiveness to the piezoelectric layer decreases, leading to a
decrease in sensor sensitivity. In addition, as shown in Reference
Examples 4 and 5, when the press-attaching conditions were
different, a difference in adhering effect of the pressurization
occurs, and thus a difference in peeling strength is verified.
INDUSTRIAL APPLICABILITY
[0149] The piezoelectric sensor of the present disclosure is used
as a biological information sensor that measures a respiration
state, a heart rate or the like in a medical field, a
rehabilitation field, a nursing field, a healthcare field, a
training field, a driver monitoring system which performs vital
sensing of an automobile, or the like.
REFERENCE SIGNS LIST
[0150] 1: biological information detecting device [0151] 10:
piezoelectric sensor [0152] 11: piezoelectric layer [0153] 12a,
12b: electrode layer [0154] 13a, 13b: protective layer [0155] 20a,
20b: wiring [0156] 30: control circuit unit [0157] 40: cover [0158]
P: subject [0159] S: pressure sensing region
* * * * *